using System;
using System.Collections.Generic;
using System.Linq;

public class Test
{
	public static void Main()
	{
    string[] things= new string[] { "100-1", "100-11", "100-3", "100-20" };
    IEnumerable<string> ordered = things
                .Select(s => new
                {
                    str = s,
                    firstPart = s.Split('-').ElementAtOrDefault(0),
                    secondPart = s.Split('-').ElementAtOrDefault(1)
                })
                .OrderBy(x => int.Parse(x.firstPart))
                .ThenBy(x => int.Parse(x.firstPart))
                .Select(x => x.str);

    foreach (string s in ordered)
        Console.WriteLine(s);
	}
}